Indium phosphide single crystal substrate and method for producing indium phosphide single crystal

Abstract

This indium phosphide single crystal substrate has a circular main surface that is virtually divided by a square lattice having a lattice spacing of 1 mm. The square lattice is composed of a plurality of lattice points existing along a first direction and a second direction orthogonal to the first direction. A set comprising dislocation densities measured at each of the lattice points has each of a first whole-surface average value which is an average value for the set and a first whole-surface standard deviation which is the standard deviation of the set, and each of the dislocation densities is classified as one of a first level, a second level, and a third level. The lattice points at which the dislocation densities classified as the second level are measured are present in a region sandwiched between the outline of a first square region and the outline of a second square region, and a second average value which is an average value for a subset comprising the dislocation densities classified as the second level is 4.0-10.0 times a first average value which is an average value for a subset comprising the dislocation densities classified as the first level.

Description

[Technical Field]

[0001] The present disclosure relates to an indium phosphide single crystal substrate and a method for producing an indium phosphide single crystal. [Background technology]

[0002] Japanese Patent Laid-Open No. 06-227898 (Patent Document 1) describes a method for doping zinc (Zn) to increase the average dislocation density on the main surface to 2000 cm -2 International Publication No. 2005 / 106083 (Patent Document 2) discloses an indium phosphide single crystal substrate (hereinafter also referred to as "InP single crystal substrate") having a diameter of 2 inches or more, which is either iron (Fe) doped or undoped, and in which the dislocation density in a region occupying 70% or more of the area of ​​the main surface is 500 cm -2 The following Non-Patent Document 1 discloses an InP single crystal substrate doped with Fe to reduce the dislocation density to 4200 cm -2 International Publication No. 2004 / 106597 (Patent Document 3) discloses an InP single crystal substrate having a diameter of 6 inches and having an average dislocation density of 5000 cm3 or less, which is doped with either Fe, sulfur (S), tin (Sn), or Zn. -2 The document discloses an InP single crystal substrate having a diameter of 75 mm or more. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 06-227898 [Patent Document 2] International Publication No. 2005 / 106083 [Patent Document 3] International Publication No. 2004 / 106597 [Non-patent literature]

[0004] [Non-Patent Document 1] T. Morishita et al., "Crystal Growth and Wafer Processing of 6-inch InP Substrate", CS Man Tech Conf. (2016) Summary of the Invention

[0005] The indium phosphide single crystal substrate according to the present disclosure is an indium phosphide single crystal substrate having a circular main surface. The main surface is a (100) plane of the indium phosphide single crystal constituting the indium phosphide single crystal substrate. The main surface is virtually divided into a square lattice with a lattice spacing of 1 mm. The square lattice is composed of a plurality of lattice points existing along a first direction and a second direction perpendicular to the first direction. A set of dislocation densities measured at each of the lattice points has a first overall average value which is the average value of the set and a first overall standard deviation which is the standard deviation of the set, and each of the dislocation densities is classified into one of a first level, a second level, and a third level. The lattice points at which the dislocation densities classified as the second level are measured are located within an area between the outline of the first square area and the outline of the second square area, and the second average value, which is the average value of a subset of the dislocation densities classified as the second level, is 4.0 to 10.0 times the first average value, which is the average value of the subset of the dislocation densities classified as the first level. The range of dislocation density classified as the first level is 0 cm -2 is greater than or equal to X0. The range of the dislocation density classified into the second level is equal to or greater than X0 and equal to or less than X1. The range of dislocation densities classified into the third level is greater than X1. The above X0 is 1 / a, and satisfies the relationship of X0>0, and the unit of the above X0 is cm -2 The a in the above 1 / a can be obtained by approximating the frequency distribution of the above set with the following formula I in a histogram where the vertical axis is the cumulative relative frequency y and the horizontal axis is the class value x. The X1 is a value obtained by adding the first full surface average value and three times the first full surface standard deviation, and satisfies the relationship of X1>X0, and the unit of X1 is cm -2 is. The x is the minimum value of each interval in the histogram, where the quotient obtained by dividing X1 by 100 is the interval width, and the unit of x is cm. -2 where y is a dimensionless number. The first square region has a square shape centered on the center point of the main surface. The first square region has vertices defined by the end points of first line segments of equal length extending from the center point in four directions equivalent to the

[0011] directions of the indium phosphide single crystal. The lengths of the first line segments are 70% of the radius of the indium phosphide single crystal substrate. The second square region has a square shape centered on the center point. The second square region has vertices defined by the end points of second line segments of equal length extending from the center point in four directions equivalent to the

[0011] directions of the indium phosphide single crystal. The lengths of the second line segments are 130% of the radius of the indium phosphide single crystal substrate. y=(1-b)×{1-exp(-ax)}+b Equation I In the above formula I, a satisfies the relationship a>0, and the unit of a is cm 2 and b is a dimensionless number that satisfies the relationship 0≦b<1. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is an explanatory diagram for schematically explaining an example of an indium phosphide single crystal substrate according to this embodiment. [Figure 2] FIG. 2 is an explanatory diagram illustrating a state in which the main surface of the indium phosphide single crystal substrate according to this embodiment is virtually divided into a square lattice with a lattice spacing of 1 mm in order to determine the dislocation density on the main surface. [Figure 3] FIG. 3 is an explanatory diagram illustrating a dislocation density distribution on the main surface of the indium phosphide single crystal substrate according to this embodiment, which is represented by lines and shaded to represent the dislocation density at each lattice point classified into the first level, second level, and third level. [Figure 4] FIG. 4 is an explanatory diagram showing lattice points at which dislocation densities classified as the second level are measured, extracted from the dislocation density distribution obtained on the main surface of the indium phosphide single crystal substrate shown in FIG. [Figure 5] FIG. 5 is an explanatory diagram that schematically illustrates a region on the main surface of the indium phosphide single crystal substrate according to this embodiment, where lattice points at which dislocation densities classified as the second level are measured exist. [Figure 6] FIG. 6 is an explanatory diagram illustrating one of four imaginary divided regions (first divided region, second divided region, third divided region, and fourth divided region) of the indium phosphide single crystal substrate shown in FIG. 4, which is divided by two straight lines perpendicular to the center point of the main surface. [Figure 7] FIG. 7 is a flowchart illustrating an example of a method for producing an indium phosphide single crystal according to this embodiment. [Figure 8] FIG. 8 is an explanatory cross-sectional view illustrating a single crystal growth apparatus used in the method for producing an indium phosphide single crystal according to this embodiment, and the internal state of the crucible of the single crystal growth apparatus in the process of obtaining an indium phosphide single crystal. [Figure 9] FIG. 9 is an explanatory diagram for explaining the main part (interface shape) of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0007] [Problem to be solved by this disclosure] For InP single crystal substrates such as those disclosed in Patent Documents 1 to 3 and Non-Patent Document 1, there have been cases where stricter yield requirements have been required in the process of obtaining semiconductor devices by growing an epitaxial film on the main surface of the substrate. Specifically, when growing an epitaxial film on the main surface of an InP single crystal substrate, the substrate may crack or chip, which is called a crack defect. Therefore, there has been a demand for reducing the probability of such a crack defect (hereinafter also referred to as the "crack defect rate"). In such cases, there is room for improvement in the InP single crystal substrates disclosed in Patent Documents 1 to 3 and Non-Patent Document 1 from the perspective of reducing the crack defect rate.

[0008] In view of the above circumstances, an object of the present disclosure is to provide an indium phosphide single crystal substrate and a method for manufacturing an indium phosphide single crystal with a reduced crack defect rate.

[0009] [Effects of this disclosure] According to the present disclosure, it is possible to provide an indium phosphide single crystal substrate and a method for manufacturing an indium phosphide single crystal with a reduced crack defect rate.

[0010] [Outline of the embodiment] An outline of an embodiment of the present disclosure will be described below. The present inventors have completed this disclosure after extensive research to solve the above-mentioned problems. Specifically, in a process of growing an indium phosphide single crystal (hereinafter also referred to as an "InP single crystal") in the crucible of a single crystal growth apparatus using a vertical boat method, the inventors focused on the following points regarding the components of the single crystal growth apparatus and the method of growing the InP single crystal. First, the heating device constituting the single crystal growth apparatus is composed of two elements (hereinafter also referred to as a "first heating region" and a "second heating region") whose outputs can be independently adjusted. Furthermore, the second heating region is configured to surround the first heating region except for its inner periphery. Furthermore, the InP single crystal is grown by maintaining the interface between the InP single crystal growing in the crucible and the indium phosphide melt at a predetermined distance below a predetermined position in the first heating region in a direction parallel to the axial direction of the crucible. The present inventors have found that when an InP single crystal substrate is manufactured from the InP single crystal ingot obtained by such a method and an epitaxial film is grown on the main surface of the substrate, the crack defect rate of the substrate is reduced, and have arrived at the present disclosure.

[0011] Next, embodiments of the present disclosure will be listed and described. [1] An indium phosphide single crystal substrate according to one embodiment of the present disclosure is an indium phosphide single crystal substrate having a circular main surface. The main surface is a (100) plane of the indium phosphide single crystal constituting the indium phosphide single crystal substrate. The main surface is virtually divided into a square lattice with a lattice spacing of 1 mm. The square lattice is composed of a plurality of lattice points existing along a first direction and a second direction perpendicular to the first direction. A set of dislocation densities measured at each of the lattice points has a first overall average value that is the average value of the set and a first overall standard deviation that is the standard deviation of the set, and each of the dislocation densities is classified into one of a first level, a second level, and a third level. The lattice points at which the dislocation densities classified as the second level are measured are located within an area between the outline of the first square area and the outline of the second square area, and the second average value, which is the average value of a subset of the dislocation densities classified as the second level, is 4.0 to 10.0 times the first average value, which is the average value of the subset of the dislocation densities classified as the first level. The range of dislocation density classified as the first level is 0 cm -2 is greater than or equal to X0. The range of the dislocation density classified into the second level is equal to or greater than X0 and equal to or less than X1. The range of dislocation densities classified into the third level is greater than X1. The above X0 is 1 / a, and satisfies the relationship of X0>0, and the unit of the above X0 is cm -2 The a in the above 1 / a can be obtained by approximating the frequency distribution of the above set with the following formula I in a histogram where the vertical axis is the cumulative relative frequency y and the horizontal axis is the class value x. The X1 is a value obtained by adding the first full surface average value and three times the first full surface standard deviation, and satisfies the relationship of X1>X0, and the unit of X1 is cm -2 is. The x is the minimum value of each interval in the histogram, where the quotient obtained by dividing X1 by 100 is the interval width, and the unit of x is cm. -2 where y is a dimensionless number. The first square region has a square shape centered on the center point of the main surface. The first square region has vertices defined by the end points of first line segments of equal length extending from the center point in four directions equivalent to the

[0011] directions of the indium phosphide single crystal. The lengths of the first line segments are 70% of the radius of the indium phosphide single crystal substrate. The second square region has a square shape centered on the center point. The second square region has vertices defined by the end points of second line segments of equal length extending from the center point in four directions equivalent to the

[0011] directions of the indium phosphide single crystal. The lengths of the second line segments are 130% of the radius of the indium phosphide single crystal substrate. y=(1-b)×{1-exp(-ax)}+b Equation I In the above formula I, a satisfies the relationship a>0, and the unit of a is cm 2 where b is a dimensionless number that satisfies the relationship 0≦b<1. An indium phosphide single crystal substrate with these characteristics can reduce the crack defect rate.

[0012] [2] The indium phosphide single crystal substrate is virtually divided into first, second, third, and fourth divided regions by two straight lines that extend from the center point in four directions equivalent to the

[0011] direction of the indium phosphide single crystal and are perpendicular to each other, 0.8×N_20 / N_0≦N_21 / N_1≦1.2×N_20 / N_0, 0.8×N_20 / N_0≦N_22 / N_2≦1.2×N_20 / N_0, 0.8×N_20 / N_0≦N_23 / N_3≦1.2×N_20 / N_0, and 0.8×N_20 / N_0≦N_24 / N_4≦1.2×N_20 / N_0 It is preferable that the following relationship is satisfied. The N_20 is the total number of the lattice points where the dislocation density classified into the second level is measured. The N_0 is the total number of the lattice points at which the dislocation density is measured. The above N_21, N_22, N_23, and N_24 are the total numbers of the lattice points at which the dislocation density classified into the second level in each of the first divided region, the second divided region, the third divided region, and the fourth divided region is measured. The above N_1, N_2, N_3, and N_4 are the total numbers of the lattice points where the dislocation density is measured in each of the first division region, the second division region, the third division region, and the fourth division region. This makes it possible to further reduce the crack defect rate.

[0013] [3] It is preferable that the second average value is 4.3 times or more and 9.0 times or less the first average value. 0.90×N_20 / N_0≦N_21 / N_1≦1.07×N_20 / N_0, 0.90×N_20 / N_0≦N_22 / N_2≦1.07×N_20 / N_0, 0.90×N_20 / N_0≦N_23 / N_3≦1.07×N_20 / N_0, and 0.90×N_20 / N_0≦N_24 / N_4≦1.07×N_20 / N_0 It is preferable to satisfy the relationship: This makes it possible to further reduce the crack defect rate.

[0014] [4] The diameter of the indium phosphide single crystal substrate is preferably 75 mm or more and 76.5 mm or less. This makes it possible to reduce the crack defect rate in large indium phosphide single crystal substrates with a diameter of 75 mm or more and 76.5 mm or less.

[0015] [5] The indium phosphide single crystal substrate contains one or more dopants selected from the group consisting of sulfur, tin, iron, and zinc, and the atomic concentration of the dopant in the indium phosphide single crystal substrate is 1.0 × 10 17 cm -3 Over 1.0 x 10 19 cm -3This makes it possible to reduce the crack defect rate in the indium phosphide single crystal substrate containing a dopant.

[0016] [6] A method for producing an indium phosphide single crystal substrate according to one embodiment of the present disclosure is a method for producing an indium phosphide single crystal using a vertical boat method, the method including the steps of: preparing a single crystal growth apparatus including at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible; placing a seed crystal in the bottom of the crucible and a bulk indium phosphide body above the seed crystal in the crucible; heating the crucible with the heating device to melt the bulk indium phosphide body and a portion of the seed crystal to obtain an indium phosphide melt and bringing the melt into contact with the remainder of the seed crystal; and growing a crystal from the melt onto the remainder of the seed crystal to obtain the indium phosphide single crystal. The heating device has a first heating region and a second heating region located on either side of the first heating region along the axial direction of the crucible. The first heating region has a first surface and a second surface. The second heating region has a third surface and a fourth surface. The third surface faces the first surface located above the first heating region in the axial direction. The fourth surface faces the second surface located below the first heating region in the axial direction. The outer periphery of the first heating region is surrounded by the second heating region. A first side surface constituting the inner periphery of the first heating region is within a cylindrical plane including a second side surface constituting the inner periphery of the second heating region. The first heating region can heat the crucible with a different output than the second heating region. The distance from the radial center of the crucible to each of the first side surface and the second side surface is 60 mm or more and 65 mm or less. In the step of obtaining the indium phosphide single crystal, when inner peripheral ends of the first surface, the second surface, the third surface, and the fourth surface in the radial direction are defined as a first position, a second position, a third position, and a fourth position, respectively, within a first cross-sectional plane that is parallel to the axial direction and includes the center of the crucible in the radial direction, a midpoint between the first position and the second position in the axial direction is defined as a fifth position, and temperatures at the third position, the fourth position, and the fifth position are defined as a first temperature, a second temperature, and a third temperature, respectively, the heating device, by using outputs of the first heating region and the second heating region, The third temperature is maintained at a temperature lower than the first temperature and lower than the second temperature. The difference between the second temperature and the third temperature is maintained at 1°C or more and 2°C or less. In a region parallel to the axial direction, 50 mm to 65 mm below the fifth position, a temperature gradient of 0.295° C. / mm to 0.305° C. / mm is formed parallel to the axial direction. In a region that is 25 mm or more and less than 50 mm below the fifth position in the axial direction, a temperature gradient of 0.235° C. / mm or more and 0.245° C. / mm or less is formed in the axial direction. In a region that is 0 mm or more and less than 25 mm below the fifth position in the axial direction, a temperature gradient of 0.095° C. / mm or more and 0.105° C. / mm or less is formed in the axial direction. In a region that is more than 0 mm and not more than 35 mm above the fifth position in the axial direction, a temperature gradient of 0.055° C. / mm or more and 0.065° C. / mm or less is formed in the axial direction. In a region that is more than 35 mm and not more than 85 mm above the fifth position in the axial direction, a temperature gradient of 0.035°C / mm or more and 0.045°C / mm or less is formed in the axial direction. The step of obtaining the indium phosphide single crystal is a step of growing the crystal by maintaining the position of the interface between the indium phosphide melt and the crystal on the inner peripheral surface of the crucible in a region 43 mm to 45 mm below the fifth position in a direction parallel to the axial direction. By using the method for producing an indium phosphide single crystal having such characteristics, it is possible to obtain an indium phosphide single crystal for producing an indium phosphide single crystal substrate with a reduced crack defect rate.

[0017] [7] It is preferable that the cross-sectional shape of the interface appearing in the first cross section includes at least a curved portion. The curved portion has, in the radial direction, one maximum point located at the center of the curved portion and two minimum points located on either side of the maximum point. In the axial direction, the positions of both ends of the curved portion are higher than the minimum points. This makes it possible to obtain indium phosphide single crystals for producing indium phosphide single crystal substrates with a reduced crack defect rate with a high yield.

[0018] [8] The curved part above is R / √2-0.1R≦D1≦R / √2+0.1R, 0.1D1≦D2, and 0.1(R-D1)≦D3 It is preferable that the following relationship is satisfied. The R is the inner radius of the crucible, and the unit of R is mm. D1 is the distance between a point on the first line segment corresponding to the maximum point and a point on the first line segment corresponding to the minimum point, which is obtained by virtually projecting the curved portion onto a straight line parallel to the radial direction, and the unit of D1 is mm. D2 is the distance between a point on the second line segment corresponding to the maximum point and a point on the second line segment corresponding to the minimum point, which is obtained by virtually projecting the curved portion onto a straight line parallel to the axial direction, and the unit of D2 is mm. When one of the two minimum points is defined as a first minimum point and the end of the two ends closer to the first minimum point is defined as a first end, D3 is the distance between a point on the second line segment corresponding to the first minimum point and a point on the second line segment corresponding to the first end, and D3 is expressed in mm. This makes it possible to obtain indium phosphide single crystals for producing indium phosphide single crystal substrates with a reduced crack defect rate at a higher yield.

[0019] [Details of the embodiment] An embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") will be described in further detail below, but the present disclosure is not limited thereto. The following description may be made with reference to the drawings, and the same or corresponding elements in the present specification and drawings will be designated by the same reference numerals, and the same description will not be repeated. Furthermore, the scale of the drawings has been adjusted appropriately to facilitate understanding of each component, and the scale of each component shown in the drawings does not necessarily coincide with the scale of the actual component.

[0020] In this specification, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and only a unit is specified for B, the unit of A and the unit of B are the same. Furthermore, when compounds and the like are expressed in this specification by chemical formulas, unless the atomic ratio is particularly limited, it is understood that any conventionally known atomic ratios are included, and they should not necessarily be limited to only those within a stoichiometric range.

[0021] In this specification, the "main surface" of an indium phosphide single crystal substrate refers to both of the two circular faces of the indium phosphide single crystal substrate. When at least one of the two faces of the indium phosphide single crystal substrate satisfies the scope of the claims of the present disclosure, the substrate falls within the technical scope of the present disclosure. Furthermore, the "face" used in the term "in-plane" in this specification refers to the "main surface." Furthermore, when the diameter of an indium phosphide single crystal substrate is described as 3 inches, this means that the diameter is 75 to 76.5 mm. The diameter can be measured using a conventionally known outer diameter measuring device such as a vernier caliper.

[0022] In this specification, "dislocation" and "dislocation density" refer to "etch pits" and "dislocation density" that are identified by applying the treatment method described below to the main surface. 2 The above-mentioned etch pits refer to the "number of pits (density)" per unit area. Although the above-mentioned etch pits are not academically synonymous with dislocations, they can be considered equivalent to dislocations in this technical field. Furthermore, the above-mentioned "dislocations" refer to "threading dislocations" present inside an indium phosphide single crystal, and the above-mentioned "threading dislocations" are known as one type of crystal defect.

[0023] In this specification, the term "crack defect rate" can be expressed as the rate at which cracks, chips, etc. occur in an indium phosphide single crystal substrate during a series of processes, from the process of growing an epitaxial film to form a semiconductor layer, etc., on the substrate to the process of fabricating a semiconductor device. The "crack defect rate" can be expressed as a percentage. Furthermore, in this specification, the term "processing yield" refers to the rate at which various semiconductor devices can be obtained from an indium phosphide single crystal substrate without cracks, chips, etc. occurring during processing. The "crack defect rate" is a factor that determines the "processing yield" and satisfies the relationship 100% - "crack defect rate" = "processing yield."

[0024] In the crystallographic descriptions in this specification, individual orientations are represented by [], collective orientations by <>, individual planes by (), and collective planes by {}. A negative index in crystallographic terms is usually represented by placing a "- (bar)" before the number, but in this specification, a negative sign is placed before the number.

[0025] [Indium phosphide single crystal substrate] The indium phosphide single crystal substrate (InP single crystal substrate) according to this embodiment is an InP single crystal substrate having a circular main surface. The main surface is a (100) plane of the indium phosphide single crystal (InP single crystal) constituting the InP single crystal substrate. The main surface is virtually divided into a square lattice with a lattice spacing of 1 mm. The square lattice is composed of a plurality of lattice points existing along a first direction and a second direction perpendicular to the first direction. A set of dislocation densities measured at each of the lattice points has a first overall average value, which is the average value of the set, and a first overall standard deviation, which is the standard deviation of the set, and each of the dislocation densities is classified into one of a first level, a second level, and a third level. The lattice points at which the dislocation densities classified as the second level are measured are located within a region between the outline of a first square region and the outline of a second square region. Furthermore, a second average value, which is the average value of a subset of the dislocation densities classified into the second level, is 4.0 to 10.0 times the first average value, which is the average value of the subset of the dislocation densities classified into the first level.

[0026] The range of dislocation density classified as the first level is 0 cm -2 The dislocation density range classified as the second level is equal to or greater than X0 and less than X1. The dislocation density range classified as the third level is greater than X1. The above X0 is 1 / a, and satisfies the relationship of X0>0, and the unit of the above X0 is cm -2 The a in the above 1 / a can be obtained by approximating the frequency distribution of the above set with the following formula I in a histogram where the vertical axis is the cumulative relative frequency y and the horizontal axis is the class value x.

[0027] y=(1-b)×{1-exp(-ax)}+b Equation I In the above formula I, a satisfies the relationship a>0, and the unit of a is cm 2 and b is a dimensionless number that satisfies the relationship 0≦b<1.

[0028] The X1 is a value obtained by adding the first full surface average value and three times the first full surface standard deviation, and satisfies the relationship of X1>X0, and the unit of X1 is cm -2 is. The x is the minimum value of each interval in the histogram, where the quotient obtained by dividing X1 by 100 is the interval width, and the unit of x is cm. -2 where y is a dimensionless number.

[0029] The first square region has a square shape centered on the center point of the main surface. The first square region has vertices defined by the end points of a first line segment of equal length extending from the center point in four directions equivalent to the

[0011] directions of the indium phosphide single crystal. The length of the first line segment is 70% of the radius of the indium phosphide single crystal substrate. The second square region has a square shape centered on the center point. The second square region has vertices defined by the end points of a second line segment of equal length extending from the center point in four directions equivalent to the

[0011] directions of the indium phosphide single crystal. The length of the second line segment is 130% of the radius of the indium phosphide single crystal substrate. An indium phosphide single crystal substrate having such characteristics can reduce the crack defect rate.

[0030] The inventors believe that the reason why the InP single crystal substrate can reduce the crack defect rate is as follows. First, the InP single crystal substrate is composed of an InP single crystal. The InP single crystal is produced using a predetermined indium phosphide single crystal growth apparatus (hereinafter also referred to simply as "single crystal growth apparatus") based on the method described in the section below titled "Method for Producing Indium Phosphide Single Crystal." Specifically, the InP single crystal is produced by using the single crystal growth apparatus to strictly control the position and shape of the interface between the InP single crystal and the indium phosphide melt (hereinafter also referred to as "InP melt") in the crucible. This allows the InP single crystal to be grown with a characteristic heat distribution in the radial direction of the crucible, thereby obtaining an InP single crystal ingot having a dislocation density distribution based on the heat distribution.

[0031] The ingot has a circular shape in plan view corresponding to the inner peripheral surface of the crucible constituting the single crystal growth apparatus. The ingot is further characterized in that a region exhibiting a second level of dislocation density (described below) is concentrated between a square region having a center point on the circular shape, extending from the center point in four directions equivalent to the

[0011] direction of the InP single crystal, and having vertices at the end points of line segments each having a length equal to 70% of the radius of the ingot, and a square region having a center point on the ingot in plan view, extending from the center point in four directions equivalent to the

[0011] direction of the InP single crystal, and having vertices at the end points of line segments each having a length equal to 130% of the radius of the InP single crystal. The inventors have discovered that an InP single crystal substrate manufactured from such an ingot has high resistance to cracking, chipping, and the like that occur due to thermal fluctuations during the growth of an epitaxial film on its main surface. It is presumed that this high resistance is obtained by the region exhibiting the second level of dislocation density relaxing the strain applied to the substrate due to thermal fluctuations during growth of an epitaxial film on the main surface. From the above, it is believed that the InP single crystal substrate according to this embodiment can reduce the crack defect rate during growth of an epitaxial film on the main surface. It should be noted that the manufacturing method of the InP single crystal substrate according to this embodiment should not be limited as long as it is an InP single crystal substrate that can reduce the crack defect rate by having the characteristics described below. Therefore, it should be noted that the manufacturing method of InP single crystal described below in the section "Method for Manufacturing Indium Phosphide Single Crystal" is preferable in terms of high production yield, but is merely one example for obtaining InP single crystals that can be used to manufacture the InP single crystal substrate according to this embodiment.

[0032] <diameter> The diameter of the InP single crystal substrate is preferably 75 mm or more and 76.5 mm or less. In other words, an InP single crystal substrate having a diameter of 75 mm or more and 76.5 mm or less is an InP single crystal substrate having a diameter of 3 inches. This reduces the crack defect rate in large-diameter InP single crystal substrates having a diameter of 75 mm or more and 76.5 mm or less. Here, the diameter of the InP single crystal substrate is determined based on the circular shape before the formation of the orientation flat (hereinafter also referred to as "OF"), index flat (hereinafter also referred to as "IF"), etc., even if the main surface does not have a geometrically circular shape due to the influence of the orientation flat (hereinafter also referred to as "OF"), index flat (hereinafter also referred to as "IF"), etc. Furthermore, as described above, the diameter of the InP single crystal substrate can be measured using a conventionally known outer diameter measuring instrument such as a vernier caliper.

[0033] <Main surface> FIG. 1 is a schematic diagram illustrating an example of an indium phosphide single crystal substrate according to this embodiment. As shown in FIG. 1, the InP single crystal substrate 1 according to this embodiment has a circular main surface 11. In this specification, the term "circular shape" used to describe the shape of the main surface includes not only a geometrically circular shape but also a shape in which the main surface does not form a geometrically circular shape due to the formation of at least one of a notch, OF, or IF on the periphery of the main surface. Here, "a shape in which the main surface does not form a geometrically circular shape" refers to a shape in which, among line segments extending from any point on the periphery of the main surface to the center of the main surface, the length of line segments extending from any point on the notch, OF, or IF to the center of the main surface is shorter. Furthermore, "a shape in which the main surface does not form a geometrically circular shape" also includes a shape in which the lengths of all line segments extending from any point on the periphery of the main surface to the center of the main surface are not necessarily the same due to the shape of the InP single crystal used as the raw material for the InP single crystal substrate. In this case, the center of the main surface refers to the position of the center of gravity. The diameter of the InP single crystal substrate refers to the length of the longest line segment extending from any point on the periphery of the InP single crystal substrate, passing through the center of the main surface, to another point on the periphery.

[0034] ((100) plane of indium phosphide single crystal) The main surface 11 is the (100) plane of the InP single crystal constituting the InP single crystal substrate 1. The (001) plane of the InP single crystal is known as one of the crystal planes commonly used to form a semiconductor layer by growing an epitaxial film on the InP single crystal substrate 1. In this disclosure, the crystal plane of the main surface is assumed to have an accuracy error of ±0.5°. For example, when the main surface is referred to as the "(100) plane" of the InP single crystal, this means that the main surface may be a just (100) plane, or may be a plane having an off-angle of -0.5 to +0.5° from the (100) plane. Whether the crystal plane of the main surface of the InP single crystal substrate is a (100) plane can be determined by a conventionally known crystal orientation measurement method.

[0035] (dislocation density) As described above, the main surface 11 of the InP single crystal substrate 1 has a dislocation density distribution that contributes to a reduction in the crack defect rate, based on the fact that the raw material InP single crystal is grown with a characteristic heat distribution in the radial direction of the crucible by the method described in the section [Method for Manufacturing Indium Phosphide Single Crystal]. The dislocation density distribution that contributes to a reduction in the crack defect rate possessed by the main surface 11 of the InP single crystal substrate 1 will be described in detail below.

[0036] 1) Classification of dislocation density measured at each lattice point into first, second or third level FIG. 2 is an explanatory diagram illustrating a state in which the main surface of an indium phosphide single crystal substrate according to this embodiment is virtually divided into a square lattice with a lattice spacing of 1 mm in order to determine the dislocation density on the main surface. As shown in FIG. 2, the main surface 11 of the InP single crystal substrate 1 is virtually divided into a square lattice G with a lattice spacing of 1 mm. The square lattice G is composed of a plurality of lattice points P located along a first direction and a second direction perpendicular to the first direction. The first and second directions can be set in any crystal orientation of the InP single crystal as long as they are mutually perpendicular on the main surface 11, which is the (100) plane of the InP single crystal. This is because the first and second directions are used only to form the square lattice G in order to determine the lattice points P on the main surface 11, which serve as measurement points for determining the dislocation density. A method for measuring the dislocation density at each lattice point P on the main surface 11 will be described later.

[0037] A set of dislocation densities measured at each lattice point P has a first full-surface average value, which is the average value of the set, and a first full-surface standard deviation, which is the standard deviation of the set. Each of the dislocation densities is classified into one of a first level, a second level, and a third level. The first full-surface average value and the first full-surface standard deviation are used to classify the dislocation densities measured at each lattice point P into the first level, the second level, and the third level, as will be described later. In particular, the first full-surface average value and the first full-surface standard deviation are used to determine X1, which is an index for classifying the dislocation density into either the second level or the third level. The first full-surface average value is specifically 30 cm -2 More than 500cm -2 The first overall standard deviation is preferably 90 cm or less. -2 More than 300cm -2 It is preferable that:

[0038] The dislocation density values ​​increase in the order of the first level, the second level, and the third level. In other words, the dislocation density values ​​satisfy the relationship of first level < second level < third level. Specifically, the range of the dislocation density of the first level is 0 cm-2 The second level of dislocation density is in the range of X0 to X1. The third level of dislocation density is in the range of X1. X0 is 1 / a, satisfying the relationship X0>0, and the unit of X0 is cm -2 The a in the above 1 / a can be obtained by approximating the frequency distribution of the above set with the following formula I in a histogram where the vertical axis is the cumulative relative frequency y and the horizontal axis is the class value x.

[0039] y=(1-b)×{1-exp(-ax)}+b Equation I In the above formula I, a satisfies the relationship a>0, and the unit of a is cm 2 and b is a dimensionless number that satisfies the relationship 0≦b<1.

[0040] The X1 is a value obtained by adding the first full surface average value and three times the first full surface standard deviation, and satisfies the relationship of X1>X0, and the unit of X1 is cm -2 The x is the minimum value of each interval of the histogram, where the quotient of X1 divided by 100 is the interval width, and the unit of x is cm -2 where y is a dimensionless number.

[0041] In this case, in the InP single crystal substrate 1, the second average value, which is the average value of the subset of dislocation densities classified as the second level, is 4.0 to 10.0 times the first average value, which is the average value of the subset of dislocation densities classified as the first level. The second average value is preferably 4.3 to 9.0 times the first average value.

[0042] Here, with reference to FIG. 2, a method for measuring the dislocation density at each of a plurality of lattice points P on the main surface 11 will be described. First, an InP single crystal is obtained, for example, based on the manufacturing method described below. This InP single crystal is subjected to conventional cutting and peripheral grinding processes to obtain an InP single crystal substrate 1 having a thickness of 1 mm, which is the measurement target. Next, the InP single crystal substrate 1 is washed with water and mirror-polished using a solution containing a diluted known abrasive. The mirror-polished InP single crystal substrate 1 is then immersed for 2 to 7 minutes in a Huber etching solution containing phosphoric acid and hydrogen bromide at a mass ratio of 2:1 at 20°C, forming corrosion pits on the main surface 11. These corrosion pits correspond to etch pits.

[0043] Next, a virtual square lattice G with a lattice spacing of 1 mm is formed by arranging 1 mm x 1 mm squares in parallel as many times as possible without overlapping each other over the entire surface of the main surface 11 of the InP single crystal substrate 1 removed from the Huber etching solution. The main surface 11 is divided by this virtual square lattice G. The square lattice G is composed of a plurality of lattice points P existing along a first direction and a second direction perpendicular to the first direction. Next, for each lattice point P, a 4 mm x 4 mm square centered on the lattice point P is defined as one field of view, and the etch pits existing within this field of view are observed using a known optical microscope, and the number of etch pits is counted. Finally, the number of etch pits existing within each field of view is counted by dividing the etch pits into 1 cm squares. 2 This converts the number of dislocations per square centimeter into the number of dislocations per square centimeter. 2 The number of etch pits per 1000 sq m can be obtained by multiplying the number of lattice points P constituting the square lattice G by the number of lattice points P. If the periphery of the main surface 11 and its surroundings appear within the above-mentioned field of view, that field of view is excluded from the calculation of dislocation density. This is because the number of etch pits in the region near the periphery of the InP single crystal substrate 1 varies greatly from substrate to substrate, and this region is not usually used as a material for optical devices.

[0044] By using the above-described method for measuring dislocation density, a set of dislocation densities measured at each lattice point P can be obtained for the InP single crystal substrate 1. Furthermore, a first overall average value, which is the average value of the set, and a first overall standard deviation, which is the standard deviation of the set, can be calculated. The dislocation densities measured at each lattice point P can be classified into one of a first level, a second level, and a third level based on the various indices described above.

[0045] 2) Regions containing lattice points where dislocation densities classified as level 2 are measured FIG. 3 is an explanatory diagram showing a dislocation density distribution on the main surface of an indium phosphide single crystal substrate according to this embodiment, where the dislocation densities at lattice points classified into the first, second, and third levels are reproduced using lines and shading. FIG. 4 is an explanatory diagram showing lattice points at which dislocation densities classified into the second level were measured, extracted from the dislocation density distribution obtained on the main surface of the indium phosphide single crystal substrate shown in FIG. 3. In FIG. 3, the dislocation density distribution based on dislocation densities measured at lattice points virtually set on the main surface of the InP single crystal substrate is represented by a reproduction using lines and shading. Specifically, the dislocation density distribution is represented by increasing concentrations of lattice points L1, L2, and L3, which are classified into the first, second, and third levels, respectively. Furthermore, FIG. 4 shows that lattice point L2, where a dislocation density classified into the second level was measured on the main surface of the InP single crystal substrate, exhibits a distribution represented by symbols (<, >) indicating inequality. That is, in the InP single crystal substrate, the lattice point L2 at which the dislocation density classified as the second level was measured is located within the region R sandwiched between the outline F1 of the first square region S1 and the outline F2 of the second square region S2 as shown in FIG. 5.

[0046] FIG. 5 is an explanatory diagram illustrating a region on the main surface of an indium phosphide single crystal substrate according to this embodiment, where lattice points at which dislocation densities classified as the second level are measured exist. In FIG. 5, the region R where lattice points L2 at which dislocation densities classified as the second level are measured exists is represented by hatching. In FIG. 5, a first square region S1 has a square shape centered on a center point O of the main surface 11. The first square region S1 has vertices at the end points of a first line segment M1 of equal length extending from the center point O in four directions equivalent to the

[0011] directions of the InP single crystal. The length of the first line segment M1 is 70% of the radius of the InP single crystal substrate 1. The second square region S2 has a square shape centered on the center point O. The second square region S2 has vertices at the end points of a second line segment M2 of equal length extending from the center point O in four directions equivalent to the

[0011] directions of the InP single crystal. The length of the second line segment M2 is 130% of the radius of the InP single crystal substrate 1.

[0047] When the lattice point L2 at which a dislocation density classified as the second level is measured is located within the region R as shown in FIG. 5 , the strain applied to the InP single crystal substrate 1 due to thermal fluctuations during epitaxial film growth is alleviated in the region R, thereby providing high resistance to cracks, chips, and the like that occur due to the thermal fluctuations. This allows the InP single crystal substrate 1 to reduce the rate of crack defects during epitaxial film growth on the main surface. The InP single crystal substrate according to this embodiment does not exclude the possibility that lattice points at which a dislocation density classified as the second level is measured may also exist outside the region R. However, in the InP single crystal substrate, the proportion of lattice points at which a dislocation density classified as the second level is measured outside the region R is preferably 20% or less of the total lattice points at which a dislocation density classified as the second level is measured.

[0048] 3) Four-fold symmetry of dislocation density distribution The InP single crystal substrate according to this embodiment is virtually divided into first, second, third, and fourth divided regions by two straight lines that extend from the center point in four directions equivalent to the

[0011] direction of the InP single crystal substrate and are perpendicular to each other. 0.8×N_20 / N_0≦N_21 / N_1≦1.2×N_20 / N_0, 0.8×N_20 / N_0≦N_22 / N_2≦1.2×N_20 / N_0, 0.8×N_20 / N_0≦N_23 / N_3≦1.2×N_20 / N_0, and 0.8×N_20 / N_0≦N_24 / N_4≦1.2×N_20 / N_0 It is preferable that the following relationship is satisfied. The N_20 is the total number of the lattice points where the dislocation density classified into the second level is measured. The N_0 is the total number of the lattice points at which the dislocation density is measured. The above N_21, N_22, N_23, and N_24 are the total numbers of the lattice points at which the dislocation density classified into the second level in each of the first divided region, the second divided region, the third divided region, and the fourth divided region is measured. The N_1, N_2, N_3, and N_4 are the total numbers of lattice points where the dislocation density is measured in each of the first division region, the second division region, the third division region, and the fourth division region. This can further reduce the crack defect rate. The following description will be given using the first division region as an example.

[0049] Fig. 6 is an explanatory diagram illustrating one of four imaginary regions (first, second, third, and fourth divided regions) of the indium phosphide single crystal substrate shown in Fig. 4, which is divided by two perpendicular lines from the center point of the main surface. As shown in Fig. 6, the first divided region B1 is one of the four imaginary regions divided by two perpendicular lines extending from the center point of the main surface in four directions equivalent to the

[0011] directions of the InP single crystal substrate 1 shown in Fig. 4. The first divided region B1 preferably satisfies the relationship 0.8 × N_20 / N_0 ≦ N_21 / N_1 ≦ 1.2 × N_20 / N_0. That is, the ratio (N_21 / N_1) of the total number of lattice points L2 classified into the second level to the total number of lattice points in the first divided region B1 is approximately the same as the ratio (N_20 / N_0) of the total number of lattice points L2 classified into the second level to the total number of lattice points on the main surface of the InP single crystal substrate, as can be seen from a comparison between Figures 4 and 6. Specifically, N_21 / N_1 is 0.8 to 1.2 times N_20 / N_0.

[0050] Furthermore, the InP single crystal substrate preferably has the same characteristics as the first dividing region B1 in each of the second dividing region, the third dividing region, and the fourth dividing region. That is, the second dividing region preferably satisfies the relationship 0.8×N_20 / N_0≦N_22 / N_2≦1.2×N_20 / N_0. The third dividing region preferably satisfies the relationship 0.8×N_20 / N_0≦N_23 / N_3≦1.2×N_20 / N_0. The fourth dividing region preferably satisfies the relationship 0.8×N_20 / N_0≦N_24 / N_4≦1.2×N_20 / N_0. It is particularly preferable that N_21 / N_1, N_22 / N_2, N_23 / N_3, and N_24 / N_4 are each 0.90 to 1.07 times N_20 / N_0.

[0051] In the InP single crystal substrate according to this embodiment, when the above-described region R contains lattice points at which dislocation densities classified as the second level are measured, and when each of the first, second, third, and fourth division regions exhibits the above-described features, the dislocation density distribution on the main surface of the InP single crystal substrate is considered to have four-fold symmetry. In this case, strain applied to the InP single crystal substrate due to thermal fluctuations when growing an epitaxial film on the main surface can be effectively alleviated in region R, which has four-fold symmetry in the dislocation density distribution. This allows the InP single crystal substrate to have a reduced crack defect rate.

[0052] <Dopants: sulfur, tin, iron or zinc, and atomic concentration> The InP single crystal substrate preferably contains one or more dopants selected from the group consisting of sulfur (S), tin (Sn), iron (Fe), and zinc (Zn). The atomic concentration of the dopant in the InP single crystal substrate is 1.0×10 17 cm -3 Over 1.0 x 10 19 cm -3 It is preferable that the concentration is less than or equal to the above. This makes it possible to reduce the crack defect rate in InP single crystal substrates containing a dopant. Specifically, it is possible to reduce the crack defect rate in n-type (electron-donating) InP single crystal substrates containing at least one of S, Sn, and Zn. Alternatively, it is possible to reduce the crack defect rate in semi-insulating InP single crystal substrates containing Fe or that are undoped. In particular, by containing the dopant in the above concentration range, it is possible to provide an InP single crystal substrate that is suitable for forming electronic devices or optical devices, for reasons such as ease of forming an n-type electrode or laminating a light-emitting layer.

[0053] The InP single crystal substrate can be doped with S, Sn, Fe, or Zn at a predetermined atomic concentration by adding S, Sn, Fe, or Zn to a crucible together with the raw material indium phosphide bulk (hereinafter also referred to as "InP bulk") when growing an InP single crystal in a manufacturing method for an InP single crystal substrate described later. The atomic concentrations of the dopants are all measured using glow discharge mass spectrometry (GDMS).

[0054] [Method for producing indium phosphide single crystal substrate] The method for producing an indium phosphide single crystal for obtaining the above-mentioned InP single crystal substrate should not be particularly limited, but from the viewpoint of good production yield, etc., the following production method is preferable. That is, the production method for an indium phosphide single crystal (production method for an InP single crystal) according to this embodiment is a production method for an InP single crystal produced using the vertical boat method. The manufacturing method includes the steps of preparing a single crystal growth apparatus having at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible; placing a seed crystal at the bottom of the crucible and placing an indium phosphide bulk body (InP bulk body) above the seed crystal in the crucible; heating the crucible with the heating device to melt the InP bulk body and a portion of the seed crystal to obtain an indium phosphide melt (hereinafter also referred to as "InP melt"), and bringing the InP melt into contact with the remainder of the seed crystal; and growing a crystal from the InP melt onto the remainder of the seed crystal to obtain the InP single crystal.

[0055] The heating device has a first heating region and a second heating region located on either side of the first heating region along the axial direction of the crucible. The first heating region has a first surface and a second surface. The second heating region has a third surface and a fourth surface. The third surface faces the first surface located above the first heating region in the axial direction. The fourth surface faces the second surface located below the first heating region in the axial direction. The outer periphery of the first heating region is surrounded by the second heating region. A first side surface constituting the inner periphery of the first heating region is within a cylindrical plane including a second side surface constituting the inner periphery of the second heating region. The first heating region can heat the crucible with a different output than the second heating region. The distance from the radial center of the crucible to each of the first side surface and the second side surface is 60 mm or more and 65 mm or less.

[0056] In this case, within a first cross-sectional plane parallel to the axial direction and including the radial center of the crucible, the inner peripheral ends of the first surface, the second surface, the third surface, and the fourth surface in the radial direction are designated as a first position, a second position, a third position, and a fourth position, respectively; the midpoint between the first position and the second position in the axial direction is designated as a fifth position; and the temperatures at the third position, the fourth position, and the fifth position are designated as a first temperature, a second temperature, and a third temperature, respectively. In this case, in the step of obtaining the InP single crystal, the heating device forms the following temperature atmosphere by the outputs of the first heating region and the second heating region. That is, The third temperature is maintained at a temperature lower than the first temperature and lower than the second temperature. The difference between the second temperature and the third temperature is maintained at 1°C or more and 2°C or less. In a region parallel to the axial direction, 50 mm to 65 mm below the fifth position, a temperature gradient of 0.295° C. / mm to 0.305° C. / mm is formed parallel to the axial direction. In a region that is 25 mm or more and less than 50 mm below the fifth position in the axial direction, a temperature gradient of 0.235° C. / mm or more and 0.245° C. / mm or less is formed in the axial direction. In a region that is 0 mm or more and less than 25 mm below the fifth position in the axial direction, a temperature gradient of 0.095° C. / mm or more and 0.105° C. / mm or less is formed in the axial direction. In a region that is more than 0 mm and not more than 35 mm above the fifth position in the axial direction, a temperature gradient of 0.055° C. / mm or more and 0.065° C. / mm or less is formed in the axial direction. In a region that is more than 35 mm and not more than 85 mm above the fifth position in the axial direction, a temperature gradient of 0.035°C / mm or more and 0.045°C / mm or less is formed in the axial direction.

[0057] Furthermore, the step of obtaining the InP single crystal is a step of growing the crystal by maintaining the position of the interface between the InP melt and the crystal on the inner peripheral surface of the crucible in a region 43 mm to 45 mm below the fifth position in a direction parallel to the axial direction. By using the method for producing an InP single crystal having these characteristics, it is possible to obtain an InP single crystal for use in obtaining an InP single crystal substrate with a reduced crack defect rate.

[0058] To achieve the goal of obtaining InP single crystal substrates with reduced cracking defects, the inventors devised a unique process for growing InP single crystals in the crucible of a single crystal growth apparatus using the vertical boat method. Specifically, they conceived the idea of ​​growing the InP single crystal with a characteristic heat distribution along the diameter of the crucible by precisely controlling the position and shape of the interface between the InP single crystal and the InP melt in the crucible. To realize this idea, the heating device constituting the single crystal growth apparatus was designed to consist of a first heating zone and a second heating zone, each capable of independently adjusting its output. The second heating zone surrounded the first heating zone except for its inner periphery. Furthermore, the interface between the InP single crystal grown in the crucible and the InP melt was maintained at a predetermined position below the first heating zone by a predetermined distance parallel to the axial direction of the crucible. This resulted in the production of an InP single crystal ingot with a dislocation density distribution based on the heat distribution. The InP single crystal substrates manufactured from the above ingots have high resistance to cracks, chips, etc. that occur due to thermal fluctuations when growing an epitaxial film on the main surface, due to the dislocation density distribution based on the above heat distribution. Based on the above, the inventors have arrived at a method for manufacturing InP single crystals that can obtain InP single crystal substrates with a reduced rate of crack defects.

[0059] The method for producing an InP single crystal according to this embodiment is a method for producing an InP single crystal using a vertical boat method. Examples of the vertical boat method include the vertical Bridgman (VB) method, the vertical gradient freeze (VGF) method, and a hybrid method combining the VB and VGF methods. From the viewpoint of producing an InP single crystal substrate having the above-described effects with a high yield, the above-described production method preferably includes steps such as those shown in the flowchart of FIG. 7. FIG. 7 is a flowchart illustrating an example of a method for producing an indium phosphide single crystal according to this embodiment. In particular, the flowchart of FIG. 7 includes an InP single crystal production step S100 and an InP single crystal substrate production step S200 for producing an InP single crystal substrate. In Figure 7, the method for manufacturing an InP single crystal substrate includes, as an InP single crystal manufacturing process S100, a step of preparing a single crystal growth apparatus having at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible (preparation process S110), a step of placing a seed crystal at the bottom of the crucible and placing an InP bulk body above the seed crystal in the crucible (raw material loading process S120), a step of heating the crucible with the heating device and melting a portion of the InP bulk body and the seed crystal to obtain an InP melt, and bringing the InP melt into contact with the remainder of the seed crystal (raw material melting process S130), and a step of growing a crystal from the InP melt onto the remainder of the seed crystal to obtain the InP single crystal (InP single crystal obtaining process S140). The preparation step S110, the raw material charging step S120, the raw material melting step S130, and the InP single crystal obtaining step S140 are performed in this order. The flowchart of FIG. 7 further includes an InP single crystal substrate manufacturing step S200, in which an InP single crystal substrate having a circular main surface is obtained from the InP single crystal. The InP single crystal substrate manufacturing step S200 includes a cutting step for cutting the InP single crystal to obtain a disk-shaped InP single crystal substrate precursor, and an outer periphery grinding step for grinding the outer periphery of the InP single crystal substrate precursor to obtain an InP single crystal substrate having a circular main surface. When carrying out the InP single crystal manufacturing method, for example, a single crystal growth apparatus 100 equipped with a crucible 5 and a heating device 7 shown in FIG. 8 can be used.8 is an explanatory cross-sectional view illustrating a single crystal growth apparatus used in the method for producing an indium phosphide single crystal according to this embodiment, and the internal state of the crucible of the single crystal growth apparatus in the process for obtaining an indium phosphide single crystal. Each step of the method for producing an InP single crystal will be described below with reference to FIGS. 7 and 8.

[0060] (Preparation step S110) The method for manufacturing an InP single crystal substrate begins with a step (preparation step S110) of preparing a single crystal growth apparatus including at least a cylindrical crucible and a heating device disposed so as to surround the outer periphery of the crucible. In preparation step S110, a single crystal growth apparatus 100, as described below, is prepared. Specifically, as shown in FIG. 8 , the single crystal growth apparatus 100 includes a cylindrical crucible 5 including a seed crystal holder 51 and a crystal growth section 52 connected to the seed crystal holder 51. The crystal growth section 52 further includes a truncated cone section 52A and a straight body section 52B. The seed crystal holder 51 is an area having a cylindrical cavity that opens to the side connected to the crystal growth section 52 and has a bottom wall formed on the opposite side. The seed crystal holder 51 can hold a seed crystal 8a in the cavity. The truncated cone section 52A of the crystal growth section 52 has a truncated cone shape and is connected to the seed crystal holder 51 at its smaller diameter side. The body portion 52B has a hollow cylindrical shape and is connected to the larger-diameter side of the truncated cone portion 52A. The crystal growth portion 52 functions to hold a solid InP bulk material therein. Furthermore, the crystal growth portion 52 of the crucible 5 functions to grow an InP single crystal 81 by solidifying an InP melt 82, which is a raw material heated to a molten state. The inclination angle from the truncated cone portion 52A to the body portion 52B of the crucible 5 is preferably 40° or less, and more preferably 20° or less. The crucible 5 can be made of various materials that can withstand the temperature at which the InP bulk material melts. For example, pyrolytic boron nitride (pBN) is conveniently used as the material for the crucible 5. The single crystal growth apparatus 100 can further include a crucible holder 6 for holding the crucible 5. The material of crucible holder 6 may be, for example, silicon carbide.

[0061] The heating device 7 is disposed to surround the outer periphery of the cylindrical crucible 5. The heating device 7 has a first heating region 71 and a second heating region 72 that sandwich the first heating region 71 along the axial direction of the crucible 5. The first heating region 71 can heat the crucible 5 at a different output from the second heating region 72. The second heating region 72 is preferably configured in multiple stages by being divided into multiple sections perpendicular to the axial direction of the crucible 5. This allows the output of the heating element in the second heating region 72 to be controlled independently for each section. Furthermore, for example, it is easy to gradually decrease the output of the heating element constituting the second heating region 72 upward along the axial direction of the crucible 5. The first heating region 71 and the second heating region 72 may include heating elements made of the same material or different materials. The first heating zone 71 and the second heating zone 72 may be heating elements made of, for example, silicon carbide, or may be heating elements made of an alloy such as a nickel-chromium alloy or an iron-chromium-aluminum alloy.

[0062] The first heating region 71 has a first surface 71a and a second surface 71b. The second heating region 72 has a third surface 72a and a fourth surface 72b. The third surface 72a faces the first surface 71a, which is located above the first heating region 71 in the axial direction. The fourth surface 72b faces the second surface 71b, which is located below the first heating region 71 in the axial direction. The outer periphery of the first heating region 71 is surrounded by the second heating region 72. The first side surface 71c, which forms the inner periphery of the first heating region 71, is located within a cylindrical plane including the second side surface 72c, which forms the inner periphery of the second heating region 72. The distance from the radial center of the crucible 5 to each of the first side surface 71c and the second side surface 72c is 60 mm or more and 65 mm or less. Preferably, the distance is 61 mm or more and 64 mm or less.

[0063] (Raw material charging process S120) The raw material charging step S120 is a step of placing a seed crystal 8a at the bottom of the crucible 5 and placing an InP bulk body above the seed crystal in the crucible 5. The purpose of the raw material charging step S120 is to place various raw materials for growing an InP single crystal in the single crystal growth apparatus 100 prepared in the preparation step S110. In the raw material charging step S120, first, the seed crystal 8a (InP seed crystal) is charged into the hollow portion of the seed crystal holding portion 51 of the crucible 5. A conventionally known method can be used to charge the seed crystal 8a into the seed crystal holding portion. Here, the cross-sectional area of ​​the seed crystal 8a is preferably 15% or more, more preferably 50% or more, of the cross-sectional area of ​​the straight body portion 52B of the crucible 5. The average dislocation density of the seed crystal 8a is 5000 cm -2 Preferably, it is 2000 cm or less. -2 It is more preferable that the following is true. It is also preferable to add a small amount of impurity atoms (S, Sn, Fe, or Zn) to the seed crystal 8a. Furthermore, multiple blocks of InP polycrystals are loaded as InP bulk bodies into the crystal growth section 52 (the truncated cone section 52A and the body section 52B) of the crucible 5 and stacked. A predetermined amount of impurity atoms (S, Sn, Fe, or Zn) may be added together with the InP bulk body. In addition, a conventionally known sealant (for example, a solid sealant made of BO (boron oxide)) may be placed on the InP bulk body.

[0064] (Raw material melting process S130) The raw material melting step S130 involves heating the crucible 5 with the heating device 7 to melt the InP bulk and a portion of the seed crystal 8a, thereby obtaining an InP melt 82, and bringing the InP melt 82 into contact with the remainder of the seed crystal 8a. The purpose of the raw material melting step S130 is to enable crystal growth of an InP single crystal to begin in the single crystal growth apparatus 100, which contains various raw materials (the seed crystal 8a and the InP bulk). In the raw material melting step S130, current is first supplied to the heating device 7, thereby heating the crucible 5, which contains the seed crystal 8a, the block of InP bulk, and a solid sealant. As a result, the solid sealant melts to form a liquid sealant 9, and the InP bulk and a portion of the seed crystal 8a melt to form the InP melt 82. The InP melt 82 then comes into contact with the remainder of the seed crystal 8a at their interface I. Furthermore, the crucible 5 is gradually pulled downward (toward the seed crystal holder 51) along its axial direction relative to the heating device 7. This creates a temperature gradient in the crucible 5 such that the temperature on the seed crystal 8a side is lower and the temperature on the InP melt 82 side is higher, making it possible to grow an InP single crystal 81 on the remaining portion of the seed crystal 8a in the next step. The speed at which the crucible 5 is pulled downward along its axial direction is preferably 10 mm / hour or less, and more preferably 5 mm / hour or less. Furthermore, when the crucible 5 is pulled downward along its axial direction, it is preferable to rotate the crucible 5 around its axis at about 5 rpm.

[0065] (Step S140 of obtaining InP single crystal) The InP single crystal growing step S140 is a step of growing an InP single crystal 81 by growing a crystal (InP single crystal 81) from the InP melt 82 on the remaining portion of the seed crystal 8a. The purpose of the InP single crystal growing step S140 is to grow the InP single crystal 81 with a characteristic heat distribution in the radial direction of the crucible 5. To achieve this purpose, in the InP single crystal growing step S140, the outputs of the first heating region 71 and the second heating region 72 constituting the heating device 7 are independently controlled to form the following temperature atmosphere, and the InP single crystal 81 is grown in this temperature atmosphere. Additionally, in the InP single crystal growing step S140, the position of the interface I between the InP melt 82 and the InP single crystal 81 on the inner peripheral surface of the crucible 5 is maintained in a region 43 mm to 45 mm below the fifth position 71f in the axial direction of the crucible 5.

[0066] In the first cross section, which is parallel to the axial direction of crucible 5 and includes the radial center of crucible 5, the inner peripheral ends of first surface 71a, second surface 71b, third surface 72a, and fourth surface 72b in the radial direction are defined as first position 71d, second position 71e, third position 72d, and fourth position 72e, respectively. The midpoint between first position 71d and second position 71e in the axial direction is defined as fifth position 71f. The temperatures at third position 72d, fourth position 72e, and fifth position 71f are defined as first temperature, second temperature, and third temperature, respectively. The cross section shown in the explanatory cross section of FIG. 8 corresponds to the "first cross section." At this time, in step S140 of obtaining an InP single crystal, the heating device 7 maintains the third temperature lower than the first temperature and lower than the second temperature by the outputs of the first heating region 71 and the second heating region 72. The heating device 7 also maintains the difference between the second temperature and the third temperature at 1°C or more and 2°C or less.

[0067] The heating device 7 forms a temperature gradient of 0.295°C / mm to 0.305°C / mm parallel to the axial direction of the crucible 5 in a region that is 50 mm to 65 mm below the fifth position 71f in the axial direction of the crucible 5. The temperature gradient is preferably 0.298°C / mm to 0.302°C / mm.

[0068] The heating device 7 forms a temperature gradient of 0.235°C / mm or more and 0.245°C / mm or less parallel to the axial direction of the crucible 5 in a region that is 25 mm or more and less than 50 mm below the fifth position 71f in the axial direction of the crucible 5. The temperature gradient is preferably 0.238°C / mm or more and 0.242°C / mm or less.

[0069] The heating device 7 forms a temperature gradient of 0.095°C / mm or more and 0.105°C / mm or less parallel to the axial direction of the crucible 5 in a region that is 0 mm or more and less than 25 mm below the fifth position 71f in the axial direction of the crucible 5. The temperature gradient is preferably 0.098°C / mm or more and 0.102°C / mm or less.

[0070] The heating device 7 forms a temperature gradient of 0.055°C / mm or more and 0.065°C / mm or less parallel to the axial direction of the crucible 5 in a region that is more than 0 mm but not more than 35 mm above the fifth position 71f in the axial direction of the crucible 5. The temperature gradient is preferably 0.058°C / mm or more and 0.062°C / mm or less.

[0071] The heating device 7 generates a temperature gradient of 0.035°C / mm or more and 0.045°C / mm or less parallel to the axial direction of the crucible 5 in a region that is more than 35 mm and not more than 85 mm above the fifth position 71f in the axial direction of the crucible 5. The temperature gradient is preferably 0.038°C / mm or more and 0.042°C / mm or less.

[0072] In step S140 of obtaining an InP single crystal, by growing an InP single crystal 81 in the above-described temperature atmosphere, it is preferable to make the interface I between the InP melt 82 in the crucible 5 and the InP single crystal 81 have a shape (cross-sectional shape) that reflects a characteristic heat distribution in the radial direction of the crucible 5, as shown in FIG. 9 . FIG. 9 is an explanatory diagram illustrating the main part (interface shape) of FIG. 8 . That is, as shown in FIG. 9 , the cross-sectional shape of the interface I that appears in the first cross section as a shape that reflects a characteristic heat distribution in the radial direction of the crucible 5 preferably includes at least a curved portion. Specifically, the curved portion preferably has one maximum point Q1 located at the center of the curved portion and two minimum points Q2 located on either side of the maximum point Q1 in the radial direction of the crucible 5. Furthermore, it is preferable that the positions of both ends E of the curved portion in the axial direction of the crucible 5 are higher than the minimum points Q2. The positions of both ends E of the curved portion correspond to the position of the interface I between the InP melt 82 and the InP single crystal 81 on the inner peripheral surface of the crucible 5 .

[0073] In addition, the curved part is R / √2-0.1R≦D1≦R / √2+0.1R, 0.1D1≦D2, and 0.1(R-D1)≦D3 It is preferable that the following relationship is satisfied. The R is the radius of the inside diameter of the crucible 5, and the unit of the R is mm. Furthermore, as shown in FIG. 9, the D1, D2, and D3 represent the following distances: D1 is the distance between a point on the first line segment that appears by virtually projecting the curved portion onto a straight line parallel to the radial direction of the crucible 5, corresponding to the maximum point Q1 on the first line segment, and a point on the first line segment that corresponds to the minimum point Q2 on the first line segment, and the unit of D1 is mm. D2 is the distance between a point on the second line segment that appears by virtually projecting the curved portion onto a straight line parallel to the axial direction of the crucible 5, corresponding to the maximum point Q1 on the second line segment, and a point on the second line segment that corresponds to the minimum point Q2 on the second line segment, and the unit of D2 is mm. Furthermore, when one of the two minimum points Q2 is the first minimum point Q21 and the end of both ends E closer to the first minimum point Q21 is the first end E1, D3 is the distance on the second line segment between a point on the second line segment corresponding to the first minimum point Q21 and a point on the second line segment corresponding to the first end E1, and the unit of D3 is mm.

[0074] When the curved portions satisfy the relationships R / √2-0.1R≦D1≦R / √2+0.1R, 0.1D1≦D2, and 0.1(R-D1)≦D3, lattice points at which dislocation densities classified as level 2 are measured can be concentrated within region R shown in Figure 5 in an InP single crystal substrate made of an InP single crystal produced by the above-mentioned production method. In particular, satisfying the relationship 0.1D1≦D2 can encourage dislocations located in the radial center of the InP single crystal to move into region R in the InP single crystal substrate in step S140 for obtaining an InP single crystal. Furthermore, satisfying the relationship 0.1(R-D1)≦D3 can encourage dislocations located in the radial outer periphery of the InP single crystal to move into region R in the InP single crystal substrate in step S140 for obtaining an InP single crystal. By satisfying the relationship R / √2-0.1R≦D1≦R / √2+0.1R, in step S140 of obtaining an InP single crystal, dislocations that have been encouraged to move into region R from the radial center and radial outer periphery of the InP single crystal can be confined within region R.

[0075] As a result, in step S140 of obtaining an InP single crystal, an ingot of InP single crystal 81 can be grown with a characteristic heat distribution in the radial direction of crucible 5. In step S140 of obtaining an InP single crystal, crucible 5 is subsequently pulled downward along its axial direction relative to heating device 7, and the position of interface I is raised toward liquid sealant 9, thereby solidifying InP melt 82 and growing InP single crystal 81 upward along the axial direction of crucible 5. Growth of InP single crystal 81 continues until solidification of InP melt 82 remaining in crystal growth portion 52 of crucible 5 is completed.

[0076] For the InP single crystal 81 obtained by the above manufacturing method, the cross-sectional shape of the interface I between the InP melt 82 and the InP single crystal 81 formed in step S140 for obtaining the InP single crystal can be confirmed by the following method. First, the ingot of the InP single crystal 81 obtained by the above manufacturing method is cut perpendicular to its growth direction to obtain a disk-shaped indium phosphide wafer (hereinafter also referred to as "InP wafer") having a thickness of 5 to 10 mm. Next, the InP wafer is cut parallel to the growth direction of the InP single crystal and so as to include the radial center of the InP wafer, thereby obtaining a rectangular cross section having a length corresponding to the diameter of the InP wafer and a width corresponding to the thickness of the InP wafer. The rectangular cross section is then etched for one hour using an etching solution made from 100 g of chromium oxide, 16 mL of hydrofluoric acid, and 544 g of pure water, and a known lamp (output: 500 W). This results in a striped pattern appearing on the rectangular cross section. Each of the lines constituting the striped pattern corresponds to the cross-sectional shape of interface I between InP melt 82 and InP single crystal 81, formed in step S140 for obtaining the InP single crystal. Therefore, by observing the striped pattern using the optical microscope (for example, trade name: "ECLIPSE (registered trademark) ME600" manufactured by Nikon Corporation), the cross-sectional shape of the interface can be confirmed. This makes it possible to confirm, for example, whether the InP single crystal being observed has grown with an interface shape that reflects a characteristic heat distribution in the radial direction of the crucible, as shown in FIG.

[0077] <Action and effect> By carrying out each of the above steps, it is possible to obtain an InP single crystal for producing an InP single crystal substrate with a reduced crack defect rate. The method for producing an InP single crystal according to this embodiment, particularly in the step of producing the InP single crystal, allows the InP single crystal to be grown with a characteristic heat distribution in the radial direction of the crucible, which is reflected in the cross-sectional shape of the interface including the curved portion described above. When an InP single crystal substrate is produced from an InP single crystal ingot obtained by this method and an epitaxial film is grown on the main surface of the substrate, the crack defect rate of the substrate can be reduced.

[0078] In the above manufacturing method, the growth direction of the InP single crystal is preferably the <100> direction. Further, when manufacturing an InP single crystal substrate from the ingot of the InP single crystal, it is preferable to obtain an InP single crystal substrate precursor described later by cutting the InP single crystal with the {100} just plane as the main surface.

[0079] 〔Method for manufacturing indium phosphide single crystal substrate〕 <InP single crystal substrate manufacturing process S200> The method for manufacturing an InP single crystal substrate according to the present embodiment includes a process of obtaining an InP single crystal substrate having a circular main surface by processing the InP single crystal obtained by the above method for manufacturing an InP single crystal. As shown in FIG. 7, the method for manufacturing the InP single crystal substrate includes an InP single crystal substrate manufacturing process S200. Specifically, the InP single crystal substrate manufacturing process S200 includes a cutting process of obtaining a disk-shaped InP single crystal substrate precursor by cutting the InP single crystal, and an outer peripheral grinding process of obtaining an InP single crystal substrate having a circular main surface by grinding the outer periphery of the InP single crystal substrate precursor. The InP single crystal substrate manufacturing process S200 includes the following cutting process, outer peripheral grinding process, and polishing process as necessary, and an InP single crystal substrate can be obtained by executing these processes in this order.

[0080] The cutting process is a process of slicing the ingot made of the InP single crystal taken out from the crucible into a wafer having a predetermined thickness in order to obtain a disk-shaped InP single crystal substrate precursor. Further, the outer peripheral grinding process is a process of obtaining an InP single crystal substrate having a circular main surface by grinding the outer periphery of the InP single crystal substrate precursor. As the cutting process and the outer peripheral grinding process, conventionally known cutting methods and outer peripheral grinding methods can be used. Further, the polishing process is a process of mirror-finishing the main surface. As the polishing process, a conventionally known polishing method can be used. By the polishing process, the main surface of the InP single crystal substrate can have a surface roughness Ra of 1 nm or less, for example, as defined in JIS B 0681-2:2018. [Example]

[0081] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these. In these examples, an InP single crystal substrate was produced using a single crystal growth apparatus as shown in Figure 8 and according to the flowchart shown in Figure 7. In the following description, Samples 11 to 13 are examples, and Samples 101 and 102 are comparative examples.

[0082] [Production of InP single crystal substrates] <Sample 11> (InP single crystal manufacturing process S100) 1) Preparation process S110 First, a single crystal growth apparatus 100 as shown in Fig. 8 was prepared. In this single crystal growth apparatus 100, the inner diameter of the straight body portion 52B of the crucible 5 was 75 mm. The inclination angle of the truncated cone portion 52A of the crucible 5 to the straight body portion 52B was 20°. Furthermore, the distances from the radial center of the crucible 5 to the first side surface 71c and the second side surface 72c of the first heating region 71 constituting the heating device 7 were each 63 mm.

[0083] 2) Raw material charging process S120 A seed crystal 8a made of InP produced by a conventional method was placed in the seed crystal holding portion 51 of the crucible 5. The cross-sectional area of ​​this seed crystal 8a was 50% of the cross-sectional area of ​​the straight body portion 52B of the crucible 5. A small amount of sulfur (S) was added to the seed crystal 8a as an impurity element. Furthermore, a plurality of lumps made of InP polycrystal were placed as InP bulk bodies in the crystal growth portion 52 (the truncated cone portion 52A and the straight body portion 52B) of the crucible 5 and stacked. The atomic concentration of the dopant at the tip end of the straight body portion 52B of the InP melt 82 described later in the crucible 5 was 2.5 × 10 18 cm -3 A small amount of S was added so that the InP bulk body was filled with a solid sealant made of boron oxide (B2O3).

[0084] 3) Raw material melting process S130 An electric current was supplied to the heating device 7 to heat the crucible 5, thereby converting the solid sealant into a liquid sealant 9, and melting a portion of the InP bulk body and the seed crystal 8a in the crucible 5 to form an InP melt 82. The InP melt 82 was then brought into contact with the remainder of the seed crystal 8a. Next, the crucible 5 was pulled downward (toward the seed crystal holder 51) along its axial direction relative to the heating device 7, thereby initiating crystal growth of an InP single crystal 81. The speed at which the crucible 5 was pulled downward along its axial direction was 3 mm / hour. During the downward pull of the crucible 5 along its axial direction, the crucible 5 was rotated around its axis at 5 rpm.

[0085] 4) Step S140 of obtaining InP single crystals Next, the outputs of the first heating region 71 and the second heating region 72 constituting the heating device 7 were independently controlled to form the following temperature atmosphere, and an InP single crystal 81 was grown under this temperature atmosphere. During this process, the position of the interface I between the InP melt 82 and the InP single crystal 81 on the inner peripheral surface of the crucible 5 was maintained at a position 44 mm below the fifth position 71f in the direction parallel to the axial direction of the crucible 5.

[0086] The temperature atmosphere is as follows. 1st temperature: 954℃ Second temperature: 950℃ Third temperature: 953℃ Temperature gradient along the axial direction of the crucible 5 in a region 50 mm or more and 65 mm or less below the fifth position 71f in parallel with the axial direction of the crucible 5: 0.301 ° C. / mm Temperature gradient along the axial direction of the crucible 5 in a region 25 mm or more and less than 50 mm below the fifth position 71f in parallel with the axial direction of the crucible 5: 0.242 ° C. / mm Temperature gradient along the axial direction of the crucible 5 in a region 0 mm or more and less than 25 mm below the fifth position 71f parallel to the axial direction of the crucible 5: 0.101 ° C. / mm Temperature gradient along the axial direction of the crucible 5 in a region parallel to the axial direction of the crucible 5, from the fifth position 71f, exceeding 0 mm and not exceeding 35 mm: 0.059 ° C. / mm Temperature gradient along the axial direction of the crucible 5 in a region that is more than 35 mm and not more than 85 mm above the fifth position 71f parallel to the axial direction of the crucible 5: 0.038°C / mm.

[0087] Subsequently, the crucible 5 was pulled downward along its axial direction relative to the heating device 7, causing the interface I between the InP single crystal 81 and the InP melt 82 to rise upward along the axial direction of the crucible 5, and the InP single crystal 81 was grown upward along the axial direction of the crucible 5. This was continued until solidification of the InP melt 82 remaining in the crucible 5 was completed. In this way, the InP single crystal 81 was obtained. Thereafter, the InP single crystal 81 was removed from the crucible 5 using a conventionally known method. In this way, an InP single crystal ingot of sample 11 having a diameter of 75 mm was obtained.

[0088] Here, the above-described method was performed on the InP single crystal ingot of sample 11 to confirm the cross-sectional shape of interface I between InP melt 82 and InP single crystal 81 formed in step S140 for obtaining the InP single crystal. Specifically, the InP single crystal ingot was cut perpendicular to its growth direction to obtain a disk-shaped InP wafer having a thickness of 5 to 10 mm. Next, a rectangular cross section having a length corresponding to the diameter of the InP wafer and a width corresponding to the thickness of the InP wafer was obtained from the InP wafer. This rectangular cross section was then etched using the etching solution and lamp under the above-described conditions to obtain a measurement sample having a striped pattern on its surface. The striped pattern was then observed with the optical microscope to identify the cross-sectional shape of interface I.

[0089] The cross-sectional shape of interface I had a curved portion as shown in Figure 9, with one maximum point Q1 located in the center of the curved portion in the radial direction of crucible 5 and two minimum points Q2 located on either side of maximum point Q1. Furthermore, in the axial direction of crucible 5, the positions of both ends E of the curved portion were higher than minimum point Q2. Furthermore, D1 to D3 were as follows: D1: 26.3 mm D2: 3.1 mm D3: 1.7mm Here, D1 refers to the distance between a point on a first line segment corresponding to the maximum point Q1 on the first line segment and a point on the first line segment corresponding to the minimum point Q2 on the first line segment, which is obtained by virtually projecting the curved portion onto a line parallel to the radial direction of the crucible 5. D2 refers to the distance between a point on a second line segment corresponding to the maximum point Q1 on the second line segment and a point on the second line segment corresponding to the minimum point Q2 on the second line segment, which is obtained by virtually projecting the curved portion onto a line parallel to the axial direction of the crucible 5. Furthermore, when one of the two minimum points Q2 is defined as a first minimum point Q21 and the end of both ends E closer to the first minimum point Q21 is defined as a first end E1, D3 refers to the distance between a point on the second line segment corresponding to the first minimum point Q21 on the second line segment and a point on the second line segment corresponding to the first end E1.

[0090] Therefore, the cross-sectional shape of interface I obtained from the InP single crystal ingot of sample 11 is R / √2-0.1R≦D1≦R / √2+0.1R, 0.1D1≦D2, and 0.1(R-D1)≦D3 The above R is the radius of the inner diameter of the crucible 5 and is 37.5 mm.

[0091] (InP single crystal substrate manufacturing process S200) Using conventionally known cutting and periphery grinding methods, the InP single crystal ingot removed from crucible 5 was cut to obtain an InP single crystal substrate precursor, and the periphery of the InP single crystal substrate precursor was further ground to produce an InP single crystal substrate having a circular main surface. As a result, an InP single crystal substrate of sample 11 having a diameter of 75 mm and a thickness of 900 μm was obtained.

[0092] <Sample 12> An InP single crystal substrate of Sample 12 having a diameter of 75 mm and a thickness of 910 μm was obtained using the same method as Sample 11, except that the second temperature in the temperature atmosphere formed in Step S140 for obtaining an InP single crystal was set to 949°C. The cross-sectional shape of Interface I, identified from the InP single crystal ingot of Sample 12 using the method described above, had a curved portion as shown in FIG. 9, with one maximum point Q1 located in the center of the curved portion in the radial direction of the crucible 5 and two minimum points Q2 located on either side of the maximum point Q1. Furthermore, in the axial direction of the crucible 5, the positions of both ends E of the curved portion were higher than the minimum point Q2. Furthermore, D1 to D3 were as follows: D1: 23.4 mm D2: 3.2 mm D3: 1.6mm.

[0093] Therefore, the cross-sectional shape of interface I obtained from the InP single crystal ingot of sample 12 is R / √2-0.1R≦D1≦R / √2+0.1R, 0.1D1≦D2, and 0.1(R-D1)≦D3 All of the relationships were met.

[0094] <Sample 13> An InP single crystal substrate of Sample 13 having a diameter of 75 mm and a thickness of 900 μm was obtained using the same method as Sample 11, except that the first temperature in the temperature atmosphere formed in Step S140 for obtaining an InP single crystal was set to 953°C. The cross-sectional shape of interface I, identified from the InP single crystal ingot of Sample 13 using the method described above, had a curved portion as shown in FIG. 9, with one maximum point Q1 located in the center of the curved portion in the radial direction of the crucible 5 and two minimum points Q2 located on either side of the maximum point Q1. Furthermore, in the axial direction of the crucible 5, the positions of both ends E of the curved portion were higher than the minimum point Q2. Furthermore, D1 to D3 were as follows: D1: 26.3 mm D2: 2.9 mm D3: 1.5mm.

[0095] Therefore, the cross-sectional shape of interface I obtained from the InP single crystal ingot of sample 12 is R / √2-0.1R≦D1≦R / √2+0.1R, 0.1D1≦D2, and 0.1(R-D1)≦D3 All of the relationships were met.

[0096] <Sample 101> An InP single crystal substrate of sample 101 having a diameter of 75 mm and a thickness of 910 μm was obtained using the same method as sample 11, except that the first temperature, second temperature, and third temperature in the temperature atmosphere formed in step S140 for obtaining an InP single crystal were all set to 954° C. The cross-sectional shape of the interface of the InP single crystal ingot of sample 101, as determined by the above-described method, had a curved portion, but only one maximum point in the center of the curved portion in the radial direction of crucible 5.

[0097] <Sample 102> An InP single crystal substrate of sample 102 having a diameter of 75 mm and a thickness of 920 μm was obtained using the same method as sample 11, except that the first temperature, second temperature, and third temperature in the temperature atmosphere formed in step S140 for obtaining an InP single crystal were all set to 953°C. Note that the cross-sectional shape of the interface of the InP single crystal ingot of sample 102, as determined by the above-mentioned method, had a curved portion, but only one maximum point in the center of the curved portion in the radial direction of crucible 5.

[0098] 〔evaluation〕 <Dislocation density> The dislocation density at each lattice point was measured on the main surfaces of the InP single crystal substrates of Samples 11 to 13, Sample 101, and Sample 102 using the method described above. Next, a first overall average value, which is the average value of the set, and a first overall standard deviation, which is the standard deviation of the set, were calculated from the set consisting of the dislocation densities measured at each of the lattice points. Furthermore, each of the dislocation densities measured at the lattice points was classified into one of the first, second, and third levels according to the various indices described above. This allowed us to determine whether or not a lattice point at which a dislocation density classified as the second level was measured was located within region R shown in Figure 5. Additionally, the ratio of the second average value, which is the average value of the subset consisting of dislocation densities classified as the second level, to the first average value, which is the average value of the subset consisting of dislocation densities classified as the first level, was calculated (second average value / first average value). These results are shown in Table 1.

[0099] Furthermore, the main surfaces of the InP single crystal substrates of Samples 11 to 13, Sample 101, and Sample 102 were divided by two mutually orthogonal lines extending from their center points in four directions equivalent to the

[0011] direction of the InP single crystal. These were designated as the first, second, third, and fourth divided regions, respectively. The ratio (N_2x / N_x) of the number of lattice points where dislocation density was measured in the second level to the total number of lattice points where dislocation density was measured in each divided region was calculated. Next, the ratio (N_20 / N_0) of the number of lattice points where dislocation density was measured in the second level to the total number of lattice points on the main surface was also calculated. From the above, the ratio [(N_2x / N_x) / (N_20 / N_0)] was calculated to determine whether the InP single crystal substrates have four-fold symmetry. The results are shown in Table 1. In Table 1, "second average value / first average value" represents the maximum value (Max), minimum value (Min), and average value (Ave) obtained for each of the first, second, third, and fourth divided regions. In Table 1, "random" means that the lattice points at which dislocation densities classified as the second level were measured were scattered on the main surface, regardless of region R.

[0100] <Processing yield> Using a specified deposition furnace, a 1.0 μm thick epitaxial film was formed on the main surface of the InP single crystal substrates of Samples 11 to 13, Sample 101, and Sample 102 by metalorganic vapor phase epitaxy (MOVPE). The InP single crystal substrates on which the epitaxial film was formed were then cooled to room temperature in the furnace and removed from the furnace. The number of cracked substrates was then divided by the number of substrates used in this evaluation, and the crack defect rate was calculated as a percentage. The crack defect rate was then subtracted from 100% to calculate the processing yield (%). The results are shown in Table 1.

[0101] [Table 1]

[0102] [Consideration] According to Table 1, in the InP single crystal substrates of Samples 11 to 13, the lattice points where dislocation densities classified as the second level were measured were located within the region between the outlines of the first and second square regions (see region R in Figure 5). In addition, the ratio of the second average value, which is the average value of the subset of dislocation densities classified as the second level, to the first average value, which is the average value of the subset of dislocation densities classified as the first level, (second average value / first average value) was within the range of 4.0 to 10.0. This resulted in a processing yield exceeding 90%. On the other hand, in the InP single crystal substrates of Samples 101 and 102, the lattice points where dislocation densities classified as the second level were measured were randomly located on the main surface. In addition, the ratio of the second average value, which is the average value of the subset of dislocation densities classified as the second level, to the first average value, which is the average value of the subset of dislocation densities classified as the first level, (second average value / first average value) was outside the range of 4.0 to 10.0. This resulted in a processing yield of 80% or less. Therefore, it can be seen that the InP single crystal substrates of Samples 11 to 13 have a reduced crack defect rate compared to the InP single crystal substrates of Samples 101 and 102.

[0103] Although the embodiments and examples of the present disclosure have been described above, it is also planned from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined.

[0104] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims. [Explanation of symbols]

[0105] 1 indium phosphide single crystal substrate (InP single crystal substrate), 11 main surface, G square lattice, O center point, P lattice point, L1 lattice point where dislocation density classified as first level was measured, L2 lattice point where dislocation density classified as second level was measured, L3 lattice point where dislocation density classified as third level was measured, M1 first line segment, M2 second line segment, S1 first square region, S2 second square region, F1 outline of first square region, F2 outline of second square region, R region, B1 first division region, S100 InP single crystal manufacturing process, S110 preparation process, S120 raw material loading process, S130 raw material melting process, S140 process of obtaining InP single crystal, S200 InP single crystal substrate manufacturing process, 100 single crystal growth apparatus, 5 crucible, 51 seed crystal holder, 52 Crystal growth region, 52A truncated cone region, 52B body region, 6 crucible holder, 7 heating device, 71 first heating region, 71a first surface, 71b second surface, 71c first side surface, 71d first position, 71e second position, 71f fifth position, 72 second heating region, 72a third surface, 72b fourth surface, 72c second side surface, 72d third position, 72e fourth position, 8a seed crystal, 81 indium phosphide single crystal (InP single crystal), 82 indium phosphide melt (InP melt), 9 liquid sealant, I interface, Q1 maximum point, Q2 minimum point, Q21 first minimum point, E both ends, E1 first end portion.

Claims

1. An indium phosphide single crystal substrate having a circular main surface, the main surface is a (100) plane of the indium phosphide single crystal constituting the indium phosphide single crystal substrate, the main surface is virtually divided by a square lattice with a lattice spacing of 1 mm, the square lattice is configured by a plurality of lattice points existing along a first direction and a second direction orthogonal to the first direction, a set of dislocation densities measured at each of the lattice points has a first overall average value which is the average value of the set and a first overall standard deviation which is the standard deviation of the set, and each of the dislocation densities is classified into one of a first level, a second level, and a third level; The lattice points at which the dislocation density classified as the second level is measured are present within an area between the outline of a first square area and the outline of a second square area, and a second average value, which is the average value of the subset of dislocation densities classified into the second level, is 4.0 times or more and 10.0 times or less than a first average value, which is the average value of the subset of dislocation densities classified into the first level; The range of the dislocation density classified into the first level is 0 cm -2 is equal to or greater than X0 and less than X0, The range of the dislocation density classified into the second level is equal to or greater than X0 and equal to or less than X1, The range of dislocation density classified into the third level is greater than X1, The X0 is 1 / a, and satisfies the relationship of X0>0, and the unit of the X0 is cm -2 a in 1 / a is found by approximating the frequency distribution of the set in a histogram with the following formula I, where y is the cumulative relative frequency on the vertical axis and x is the class value on the horizontal axis: The X1 is a value obtained by adding the first overall average value and three times the first overall standard deviation, and satisfies the relationship of X1>X0, and the unit of X1 is cm -2 and The x is the minimum value of each interval of the histogram, the interval width of which is the quotient of X1 divided by 100, and the unit of x is cm -2 and y is a dimensionless number, the first square region has a square shape centered at the center point of the main surface, the first square region has, as vertices, end points of first line segments of equal length extending from the center point in four directions equivalent to the [011] direction of the indium phosphide single crystal; the length of the first line segment is 70% of the radius of the indium phosphide single crystal substrate; the second square region has a square shape centered at the central point, the second square region has, as vertices, end points of second line segments of equal length extending from the center point in four directions equivalent to the [011] direction of the indium phosphide single crystal; The length of the second line segment is 130% of the radius of the indium phosphide single crystal substrate. y=(1-b)×{1-exp(-ax)}+b Formula I In the above formula I, a satisfies the relationship of a>0, and the unit of a is cm 2 and b is a dimensionless number that satisfies the relationship 0≦b<1.

2. The indium phosphide single crystal substrate is In a first divided region, a second divided region, a third divided region, and a fourth divided region which are virtually divided by two straight lines which extend from the center point in four directions equivalent to the [011] direction of the indium phosphide single crystal and are perpendicular to each other, 0.8×N_20 / N_0≦N_21 / N_1≦1.2×N_20 / N_0, 0.8×N_20 / N_0≦N_22 / N_2≦1.2×N_20 / N_0, 0.8×N_20 / N_0≦N_23 / N_3≦1.2×N_20 / N_0, and 0.8×N_20 / N_0≦N_24 / N_4≦1.2×N_20 / N_0 Fulfilling the relationship, N_20 is the total number of the lattice points at which the dislocation density classified into the second level is measured, N_0 is the total number of the lattice points at which the dislocation density is measured, N_21, N_22, N_23, and N_24 are the total numbers of the lattice points at which the dislocation densities classified into the second level are measured in each of the first division region, the second division region, the third division region, and the fourth division region, 2. The indium phosphide single crystal substrate according to claim 1, wherein N_1, N_2, N_3, and N_4 are the total numbers of the lattice points at which the dislocation density is measured in each of the first division region, the second division region, the third division region, and the fourth division region.

3. the second average value is 4.3 times or more and 9.0 times or less than the first average value, In the first divided region, the second divided region, the third divided region, and the fourth divided region, 0.90×N_20 / N_0≦N_21 / N_1≦1.07×N_20 / N_0, 0.90×N_20 / N_0≦N_22 / N_2≦1.07×N_20 / N_0, 0.90 × N_20 / N_0 ≦ N_23 / N_3 ≦ 1.07 × N_20 / N_0, and 0.90 × N_20 / N_0 ≦ N_24 / N_4 ≦ 1.07 × N_20 / N_0 3. The indium phosphide single crystal substrate according to claim 2, which satisfies the relationship:

4. 4. The indium phosphide single crystal substrate according to claim 1, wherein the diameter of the indium phosphide single crystal substrate is 75 mm or more and 76.5 mm or less.

5. the indium phosphide single crystal substrate contains one or more dopants selected from the group consisting of sulfur, tin, iron, and zinc; The atomic concentration of the dopant in the indium phosphide single crystal substrate is 1.0×10 17 cm -3 Above 1.0 x 10 19 cm -3 4. The indium phosphide single crystal substrate according to claim 1, wherein:

6. A method for producing an indium phosphide single crystal using a vertical boat method, comprising: The manufacturing method includes: A step of preparing a single crystal growth apparatus including at least a cylindrical crucible and a heating device disposed so as to surround the outer periphery of the crucible; placing a seed crystal at the bottom of the crucible and placing an indium phosphide bulk body above the seed crystal in the crucible; heating the crucible with the heating device to melt the indium phosphide bulk body and a portion of the seed crystal to obtain an indium phosphide melt, and bringing the indium phosphide melt into contact with the remainder of the seed crystal; and growing a crystal from the indium phosphide melt on the remainder of the seed crystal to obtain the indium phosphide single crystal; the heating device has a first heating region and a second heating region located on either side of the first heating region along the axial direction of the crucible, the first heating region has a first surface and a second surface; the second heating region has a third surface and a fourth surface; the third surface faces the first surface located above the first heating region in the axial direction, the fourth surface faces the second surface located below the first heating region in the axial direction, The outer periphery of the first heating region is surrounded by the second heating region, a first side surface that defines an inner periphery of the first heating region is located within a cylindrical plane that includes a second side surface that defines an inner periphery of the second heating region; the first heating region is capable of heating the crucible at an output different from that of the second heating region; a distance from a radial center of the crucible to each of the first side surface and the second side surface is 60 mm or more and 65 mm or less; In the step of obtaining the indium phosphide single crystal, when inner peripheral ends of the first surface, the second surface, the third surface, and the fourth surface in the radial direction are respectively designated as a first position, a second position, a third position, and a fourth position within a first cross-sectional plane that is parallel to the axial direction and includes the center of the crucible in the radial direction, a midpoint between the first position and the second position in the axial direction is designated as a fifth position, and temperatures at the third position, the fourth position, and the fifth position are respectively designated as a first temperature, a second temperature, and a third temperature, the heating device, by using outputs of the first heating region and the second heating region, maintaining the third temperature lower than the first temperature and lower than the second temperature; Maintaining a difference between the second temperature and the third temperature of 1°C or more and 2°C or less; and forming a temperature gradient of 0.295° C. / mm or more and 0.305° C. / mm or less in parallel to the axial direction in a region that is 50 mm or more and 65 mm or less below the fifth position in parallel to the axial direction; forming a temperature gradient of 0.235° C. / mm or more and 0.245° C. / mm or less parallel to the axial direction of the crucible in a region that is 25 mm or more and less than 50 mm below the fifth position parallel to the axial direction; forming a temperature gradient of 0.095° C. / mm or more and 0.105° C. / mm or less in parallel to the axial direction in a region that is 0 mm or more and less than 25 mm below the fifth position in parallel to the axial direction; In a region that is more than 0 mm and not more than 35 mm above the fifth position in the axial direction, a temperature gradient of 0.055° C. / mm or more and 0.065° C. / mm or less is formed in the axial direction; In a region that is more than 35 mm and not more than 85 mm above the fifth position in the axial direction, a temperature gradient of 0.035° C. / mm or more and 0.045° C. / mm or less is formed in the axial direction; the step of obtaining the indium phosphide single crystal is a step of growing the crystal by maintaining the position of the interface between the indium phosphide melt and the crystal on the inner peripheral surface of the crucible in a region that is 43 mm to 45 mm below the fifth position in a direction parallel to the axial direction.

7. a cross-sectional shape of the interface appearing in the first cross section includes at least a curved portion; The curved portion is In the radial direction, the curved portion has one maximum point located at the center thereof and two minimum points located on both sides of the maximum point, The method for producing an indium phosphide single crystal according to claim 6 , wherein the positions of both ends of the curved portion in the axial direction are higher than the minimum point.

8. The curved portion is R / √2-0.1R≦D1≦R / √2+0.1R, 0.1D1≦D2, and 0.1(R-D1)≦D3 Fulfilling the relationship, R is the radius of the inner diameter of the crucible, and the unit of R is mm. D1 is a distance between a point on a first line segment that appears by virtually projecting the curved portion onto a straight line parallel to the radial direction, the point corresponding to the maximum point on the first line segment, and a point on the first line segment that corresponds to the minimum point on the first line segment, and the unit of D1 is mm. D2 is a distance between a point on a second line segment that appears by virtually projecting the curved portion onto a straight line parallel to the axial direction, the point corresponding to the maximum point on the second line segment, and a point on the second line segment that corresponds to the minimum point on the second line segment, and the unit of D2 is mm.

8. The method for producing an indium phosphide single crystal according to claim 7, wherein when one of the two minimum points is defined as a first minimum point and one of the ends closer to the first minimum point is defined as a first end, D3 is a distance on the second line segment between a point on the second line segment corresponding to the first minimum point and a point on the second line segment corresponding to the first end, and D3 is expressed in mm.

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